Spectroscopy on light exotic nuclei

1
Spectroscopy on light exotic nuclei
H.Sakurai Univ. of Tokyo
2
RIKEN Facility
In-flight RI beam production
RIKEN Ring Cyclotron
RIPS (Riken Projectile Fragment Separator)
Primary beam E/A64-135 MeV
RI beam E/A30-90 MeV
Experiment
K540
production target
3
Progress of Research Opportunities with RI Beams
Construction of a dedicated facility for RI beam
production via the projectile fragmentation
4
SRC K2500 350400 A MeV 350A MeV U
5
RIBFRI Beam Factory the 3rd generation facility
RIBF
RIBF
RIBF
RI beams A lt 200 E 250A MeV
RIPS
in 2007
present facility
RI beams A lt 50 E 50A MeV
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Investigation on Nuclear Structure via In-beam g
Spectroscopy
- Magicity Loss and Collective Motion -
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Experimental setup for in-beam gamma
spectroscopywith fast RI beams
Charged particle detectors
particle identification for ejectiles
gamma-ray detector array
2
observation of de-excited g rays
?
g-ray energy and emission angle for Doppler
correction
0
RI beam
NaI detector
50 A MeV
target
E
?
?
inverse reaction high energy beam -gt thick
target kinematical focusing -gt high efficiency
beam
Doppler-shift corrected spectrum
8
Investigation on Nuclear Structure via In-beam g
Spectroscopy
- Magicity Loss and Collective Motion -
Present Facility RIPS 1. Magicity loss at N20
2. 16C The New Facility RIBF 3. Future
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Investigation for the island-of-inversion region
How is the region extended ? lower Z and larger N
Search for new isotopes Particle stability
31Ne, 31F In-beam gamma spectroscopy B(E2)
lt- CEX 32Mg, 34Mg E(2), E(4) lt-
Two step fragmentation 34Mg
34Mg
32Mg
28
8
31F
34Mg has a larger collectivity than 32Mg.
30Ne
20
27F
In-beam gamma spectroscopy
Why 31F is particle bound ? How large
collectivity at Z9, 10?
proton inelastic scattering 30Ne E(2)
27F bound excited states
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The first excited state of 30Ne via (p,p)
Yanagisawa et al., Phys. Lett. B 566 (2003) 84
30Ne Intensity 0.2 /sec
N20 Isotone
Luminosity Enhancement via Liquid Hydrogen
target
data
200 mg/cm2
0hw
p Pb
E(21) keV
Number of target nuclei
200 1
2hw
29Ne
885
791
28Ne
Counts/40keV
30Ne
32Mg
34Si
36S
E(2, 30Ne) lt E(2, 32Mg) 30Ne has a larger
collectivity than 32Mg?
Energy keV
11
Bound excited states in 27F
Elekes et al., PLB 599 (2004) 17
One bound excited state predicted via
sdpf-shell model lt- neutron excitation across
N20
27F
2.0
Sn1.4 MeV
1.1
1/2
5/2
sd
sdpf
Otsuka et al.
Brown
Two bound excited states for 25,26,27F via
p(27F, 25,26,27F g)
proton contribution across Z8 gap??
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Investigation on Nuclear Structure via In-beam g
Spectroscopy
- Magicity Loss and Collective Motion -
Present Facility RIPS 1. Magicity loss at N20
2. 16C The New Facility RIBF 3. Future
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B(E2) measurement for the light mass region
lifetime
unstable nuclei
stable nuclei
B(E2)
Coul. Ex.
28Si
30Si
32Si
34Si
36Si
38Si
40Si
32Mg
34Mg
36Mg
38Mg
24Mg
26Mg
28Mg
30Mg
t
CEX
26Ne
28Ne
30Ne
32Ne
34Ne
20Ne
22Ne
24Ne
16O
18O
20O
22O
24O
Zlt8
12C
14C
16C
18C
20C
22C
10Be
12Be
14Be
Zlt8 Coulomb Ex. lt Nuclear Ex.
No data for the neutron-rich Be and C isotopes
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Density distribution of the C isotopes by AMD
Y. Kanada-Enyo and H. Horiuchi, Prog. Theor.
Phys. 142,205(2001)
proton
proton
neutron
neutron
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B(E2) measurement for 16C via a new techniques
lifetime
unstable nuclei
stable nuclei
B(E2)
Coul. Ex.
28Si
30Si
32Si
34Si
36Si
38Si
40Si
2
32Mg
34Mg
36Mg
38Mg
24Mg
26Mg
28Mg
30Mg
t
CEX
26Ne
28Ne
30Ne
32Ne
34Ne
20Ne
22Ne
24Ne
0
16O
18O
20O
22O
24O
Zlt8
12C
14C
16C
18C
20C
22C
Zlt8 Coulomb Ex. lt Nuclear Ex.

10Be
12Be
14Be
New method appropriate for fast RI beam should be
developed Recoil-Shadow-Method
Lifetime measurement of 2 state
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Recoil-shadow-method
R1, R2 gamma detectors

• Inelastic Scattering of RI beams
• High velocity (b0.3)
• al bgtc
• 1.0 cm (t100ps, b0.3)
• Thick lead shield
• ashadowing for g-rays
• in delayed emission
• e exp (- m l ) m attenuation coeff.
• l path length in lead

target (9Be)
R1/R2 ratio has mean life dependence
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Anomalously hindered B(E2) of 16C
N. Imai et al, Phys.Rev.Lett. 92,062501(04)
t 77 /- 14 (stat.) /- 19 (syst.) ps
B(E2 2 -gt 0)
0.63 e2fm4 0.26 W.u.
bem 0.14
Quantum liquid drop model
S. Raman et.al.,PRC37, 805 (88).
B(E2)sys6.47Z2A-0.69E(2)-1
B(E2) /B(E2)sys0.03
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Neutron contribution to the 2 state??
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Proton Inelastic Scattering on 16C
H.J. Ong et al, to be submitted to PRL
proton the most sensitive probe for neutron
matter
In-beam g technique to obtain angular integrated
cross section
s 24 /- 4 mb
DWBA analysis (ECIS)
bpp 0.50 /- 0.07 gt bem 0.14 dpp 1.42
/- 0.21 fm
Errors include optical potential dependences
(CH89, p12C, p16O), too
bpp/bsys
bpp/bsys 1
bsys 466A-1E(2)-1/2 Ramans systematics
16C
Magnitude of bpp for 16C is the same as those
of other nuclei.
10
20
50
100
200
mass number A
Neutron-dominant collective motion
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Disentanglement of proton and neutron
contributions
1.Combination of bem and bpp, based on
Bernsteins prescription
bn/bem Mn/Mp / (N/Z) 4.0 /- 1.4
Mn/Mp / (N/Z)
H.J. Ong et al, to be submitted to PRL
10
20
50
100
200
mass number A
2. Interference of nuclear and Coulomb
excitation in inelastic scattering on Pb
Elekes et al., Phys.Lett.B 586, 34 (2004)
bn/bem4.6 /- 1
bem B(E2i)0.28(6) W.u.
Imai et al. B(E2i)0.26 W.u.
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New type of collective motion?
exotic picture for 16C case
classical picture
TWO quantum liquid drops
ONE quantum liquid drop
one-body nuclear matter
proton matter
neutron matter
proton- and neutron matters contributions to
collective motion are same.
bn/bem4 5
Large contribution by neutron matter, not by
proton matter
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Why B(E2) is so small??
Effective charges ?
Q-moments of 15,17B Izumi et al., PLB366
(1996)51 Ogawa et al., PRC67(2003)064308
en/e 0 due to weak binding of neutrons?
Z6 magic number ?
Shell gaps from mass information proton-shell
12 MeV a large gap between p3/2
and p1/2 neutron-shell lt 1 MeV
Based on Audi et al., NPA 729(2003)337
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Proton and neutron shell gaps from mass
information
H.Sakurai ENAM04
proton shell gap S2p(Z,N)-S2p(Z2,N)
MeV
p1/2
Z6
p3/2
proton number
16C
N10
neutron number
neutron shell gap S2n(Z,N)-S2n(Z,N2)
MeV
Z6
proton number
16C
N10
p1/2
s1/2
d5/2
neutron number
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Investigation on Nuclear Structure via In-beam g
Spectroscopy
- Magicity Loss and Collective Motion -
Present Facility RIPS 1. Magicity loss at N20
2. 16C The New Facility RIBF 3. Future
25
Exploration towards heavier and more proton-rich
/neutron-rich region
to produce a lot of data for unified pictures
RIBF
RIPS
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Subjects of nuclear structure and collectivity
CEX -gt B(E2) (p,p) -gt b2
B(E2)-1 1/W.u
82
100Sn double magicity?
208Pb
126
deformation region?
48Ni double magicity?
proton number
50
132Sn
N82 magicity?
82
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78Ni double magicity?
50
20
N34 new magicity?
N28 magicity?
2001
20
neutron number
27
Higher excited states and higher spin statesfor
exotic phenomena of collectivity?
not only low lying states but also ...
for intermediate and heavy mass system
neutron skins ? collectivity originated
from neutrons in skin pairing ?
rotation energy v.s. pairing energy exotic modes
? originated from two asymmetric
liquids ...
J, Ex
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Summary
Island of inversion
30Ne E(2, 30Ne) lt E(2, 32Mg)
30Ne has a larger collectivity than 32Mg? 27F
two bound excited states. proton
contributions across Z8?
Anomalous quadrupole collectivity of 16C
B(E2), (p,p), Interference
bn/bem 45 gt 1
neutron-dominant collectivity How about 18C, 20C
?
proton matter
neutron matter
For future
Any exotic collective motion proposed
in medium- and heavy-mass region?